It is well known that laundry detergent compositions for use in washing machines having a closed drum, such as European-type front loading automatic washing machines, require foam control to prevent overfoaming. Foam control granules in which mobile liquid or viscous-liquid hydrophobic foam control agents such as silicone oil or hydrocarbons are sorbed onto a particulate carrier material are well known in the art.
The main problem associated with such granules is to achieve a good balance between delivery of the mobile hydrophobic foam control agent during the wash cycle and storage stability. The hydrophobic foam control agent must be retained in or on the carrier material during storage, but released efficiently from the carrier material during the wash cycle. EP 266 863A (Unilever) discloses a foam control granule in which a mobile hydrophobic foam control agent, especially a silicone oil, is sorbed onto a fine-pored inorganic carrier based on sodium carbonate, preferably light soda ash, crystal-growth-modified sodium sesquicarbonate or crystal-growth-modified Burkeite. These carrier materials combine a high pore volume with a small pore diameter and therefore have a high capacity for retaining the foam control agent. They are also highly water-soluble and release the foam control agent rapidly and effectively during the wash cycle.
These granules differ from other known granules in which the carrier material, for example, a native or modified starch, consists of very small primary-particles, for example, having a particle size of 1-10 .mu.m, and the hydrophobic foam control agent, generally plus one or more binders, is used to build up larger particles by agglomeration. In foam control granules of that type, the primary particles of the carrier material are essentially non-porous and the silicone oil is adsorbed onto their surfaces, that is to say, the porosity of the final granules occupied by the silicone oil is inter-particle porosity.
In the foam control granules with which the present invention is concerned, the mobile foam control agent is predominantly within the intraparticle pore system of the carrier material, although a limited amount of agglomeration may also occur. The intra-particle pore structure allows entrapment of the foam control agent within the primary particles of the carrier material, but still gives rapid and efficient delivery of the foam control agents in the wash at both high and low wash temperatures.
The small pore size also means that the foam control agent is released in the wash in the form of especially small particles or droplets, which increases its foam control efficiency.
These granules show excellent foam control and storage stability within detergent compositions. However, it has been found that when granules using the preferred carrier material of light soda ash are prepared by high speed mixing and granulation, the flow properties of the granules themselves are not always ideal, and some tendency towards caking has been observed. This can cause problems in the bulk handling and transportation of the granules prior to their incorporation in detergent products.
It has now unexpectedly been discovered that the granules have significantly better flow properties if a controlled amount of water is added after the mixing and granulation step.